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Application of Polarization of Fluorescence Technique to Protein Studies. II. The Rotatory Properties of -Casein¹

Departments of Dairy Technology and Chemistry The Ohio State University, Columbus

ABSTRACT

The polarization of fluorescence technique was used to study certain properties of -casein prepared either by the urea-fractionation method or a constant-pH method. Dye-conjugated preparations of each of these caseins responded similarly to the application of the polarization of fluorescence method, in that both yielded curves with negative slopes, but with the urea-fractionated -casein giving slightly steeper slopes. These -caseins were found to be generally similar, with only minor differences being observed in their electrophoretic and ultracentrifuge patterns.

The properties of constant-pH -casein as determined by the polarization of fluorescence method were altered slightly by addition of sucrose, disodium EDTA, calcium, and phosphate, but treatment with a cation exchange resin at pH 6.5 and 11.0 was essentially without effect. The polarization of fluorescence properties of this protein were shown to be dependent upon temperature and pH, yielding positive slopes for reciprocal polarization vs. temperature/viscosity curves at pH 10.9 and above.

The monomer-polymer interaction for -casein was investigated and values for the mole fraction of each, as a function of pH and temperature, were approximated.

¹ Article 362, Department of Dairy Technology. Supported in part by University grants-in-aid and by a grant from the National Institutes of Health (U. S. Public Health Service).